1. Field of the Invention
The present invention relates in general to seat slide devices for a motor vehicle, and more particularly to seat slide devices of a type which can adjust the fore-and-aft position of a seat.
2. Description of the Prior Art
In order to clarify the task of the present invention, one conventional seat slide device will be described with reference to FIG. 5 of the accompanying drawings, which device is disclosed in U.S. Pat. No. 4,813,643 granted on Mar. 21, 1989.
The device comprises a lower rail 102 which is secured to a vehicle floor through front and rear mounting brackets 101a and 101b. An elongate lock plate 106 is secured to a side portion of the lower rail 102 and extends along the same. The lock plate 106 is formed with a plurality of aligned and evenly spaced openings 106a.
An upper rail 103 which carries thereon a seat (not shown) is slidably disposed on the lower rail 102. The upper rail 103 has a larger bracket 104 secured thereto. The larger bracket 104 has a curled portion 104a by which a rear portion of a control rod 105 is rotatably supported. A smaller bracket 108 is secured to a front portion of the upper rail 103 to rotatably support the control rod 105. A front portion of the control rod 105 is bent to form a handle 105a.
A latch member 107 is secured to the control rod 105 at the larger bracket 104. Thus, the latch member 107 and the control rod 105 rotate like an integral unit. The latch member 107 has at its free end two latch pawls which are sized to be latchingly engageable with neighboring two of the openings 106a of the lock plate 106.
A coil spring 109 is disposed about the rear end of the control rod 105 and arranged to bias the control rod 105 to rotate in a clockwise direction in FIG. 5, that is, in a direction to achieve a latched engagement of the latch member 107 with the lock plate 106.
Upon requirement of position adjustment of the seat, the handle 105a of the control rod 105 is manipulated to pivot the rod 105 in a counterclockwise direction in FIG. 5 against the biasing force of the coil spring 109. With this, the latched engagement of the latch member 107 with the lock plate 106 is cancelled thereby permitting a free movement of the upper rail 103 (that is, the seat mounted on the upper rail 103) relative to the lower rail 102. When the upper rail 103 comes to a new desired position, the handle 105a is released from an operator's hand. With this, due to the biasing force of the coil spring 109, the latch pawls of the latch member 107 are brought into latching engagement with new neighboring two of the openings 106a of the lock plate 106. With this, the seat becomes locked at the new desired position.
However, the seat slide device of the above-mentioned type has the following drawbacks.
That is, due to its inherent construction, it is very difficult to reduce the weight of the device without sacrificing the mechanical strength of the same.
In fact, hitherto, an attempt has been made for reducing the weight of the device by using aluminium alloy as a material for the lower and upper rails. However, due to the nature of aluminium alloy, the seat slide device produced has failed to exhibit a satisfied mechanical strength.